Pakistan may have played a critical role in helping North Korea build nuclear weapons capable of threatening Japan and even the United States, the International Institute for Strategic Studies says in its report on North Korea's weapons programme.

The report of the London-based IISS has been published in the same week that Pakistan's security agencies have been questioning leading scientists and military officers about the role they may have played in exporting nuclear weapons technology to Libya, Iran and North Korea.

Citing US press reports, the IISS says, "US intelligence believes that Pakistan may have provided North Korea with nuclear weapons design information and even supplies of high enriched uranium under the missile-for-nuclear [tech] barter agreement of the late 1990s.

"With North Korean and Pakistani nuclear and missile personnel apparently working closely together for several years, it is plausible that some discussion of weaponisation would take place."

The IISS identifies the father of the Pakistani nuclear programme, India-born Abdul Qadeer Khan, as the key contact between Pakistan and North Korea.

Describing his work for the European URENCO consortium, where he was employed as a metallurgist, the IISS report says he "obtained the designs for at least three types of centrifuges.

"The most advanced was the G-2, a German-designed, super critical centrifuge" that eventually "became the work horse of Pakistan's nuclear weapons programme after Khan returned home.

"By the 1990s Khan was also in charge of Pakistan's efforts to develop a nuclear-capable, long range, liquid-fuelled missile. Consequently, he became the principal point of contact with regard to nuclear and missile co-operation with North Korea, reportedly making numerous trips to North Korea beginning in the late 1990s."

The investigation by Pakistani security officers follows last month's disclosure by Saif ul Islam, the son of Libyan President Colonel Muammar Gaddafi, that Tripoli also imported some nuclear components from Pakistan.

Since then, the Vienna-based International Atomic Energy Agency has unearthed evidence that uranium centrifuges discovered in Iran appear to be based on a Pakistani design.

The spate of claims about Pakistan's role in proliferation of nuclear weapons prompted Pakistan's High Commissioner in London Dr Maleeha Lodhi to insist earlier this week that her government is committed not to transfer nuclear technology to other countries, claiming that action would be taken against any individuals in her country who breach this commitment.

Addressing a seminar in London, Dr Lodhi said, "We are committed not to transfer nuclear technology. Certain facts have been brought to our attention and, as a result, there is an ongoing investigation.

"As a country that is committed to non-proliferation, we will take action against any individuals involved. The law will take its course, but let us not prejudge that anyone is guilty. Once the inquiry is concluded, we will decide what to do."

Meanwhile, the Pakistan Peoples Party headed by Benazir Bhutto has called for a parliamentary inquiry into how individual scientists could be responsible for nuclear exports.

"A full debate is necessary to see whether the Pak scientists did export technology for personal greed or whether they were being made scapegoats to save General Musharraf and his clique," a PPP spokesman said.

He added that the PPP had asked "whether General Musharraf was the in charge of nuclear control and command when the nuclear transfers took place...If so, then General Musharraf must answer the nation for jeopardising the nuclear assets.

"It may be recalled that in 1988, when the PPP assumed power, there was great international pressure for Pakistan to roll back its nuclear programme. The government of Benazir Bhutto initiated talks with concerned players and produced a consensus between the president, the prime minister and the armed forces as well as the international community to save the nuclear assets.

"Under this consensus, the Benazir Nuclear Doctrine was enunciated in which no export of nuclear technology was one of the guarantees that Islamabad gave the world community to save Pakistan's nuclear programme from a roll back.

"It was therefore shocking that as per the admission by Pak foreign office, export of nuclear technology did take place.

"Nation must know the exact dates when alleged export of nuclear technology took place. It is suspected that this export of nuclear technology took place when General Musharraf was the army chief and later chief executive. However, regime is refusing to release details which is causing more suspicions to arise.

"As army chief, General Musharraf would have been in charge of command and control of the nuclear facilities structure put formally into place in the second PPP government in 1993 to prevent individuals from acting individually.

"Musharraf has denied that his regime authorised transfers of nuclear technology to Iran, Libya, and North Korea. His representatives in the foreign office said it was the action of individuals."